FLUID DESIGN TO MEET RESERVOIR ISSUES-A PROCESS

J.MASIKEWICH B.BENNION

this article begins on the next page FF THE PETROLEUM SOCIETY PAPER 97-114 Fluid Design to Meet Reservoir Issues- A Process J. Masikewich Q'Max Solutions Inc. B.Bennion Hycal Energy Research Laboratories Ltd. This paper is to be presented at the 48th Annual Technical Meeting of The Petroleum Society in Calgary, Alberta, Canada, June 8 - 11, 1997. Discussion of this paper is invited and may be presented at the meeting if filed in writing with the technical program chairman prior to the conclusion of the meeting. This paper and any discussion filed will beconsidered for publication in CIM journals. Publication rights are reserved. This is a pre-print and is subject to correction. ABSTRACT stimulation The process may lead to innovation - resulting in new systems or products. It may be applied when As open hole completion's, horizontal wells, multi-lateralsdesigning workover and completion fluids or for drill-in and underbalanced drilling become more common Place, fluids including overbalanced or underbalanced greater emphasis is being placed on the selection and design applications. of drilling and completion fluids. The problem of assessing fluid compatibility with hydrocarbon reservoirs is ongoing and usually unique to eachreservoir. This problem becomes INTRODUCTION most visible after resources have been expended to drill, with unsatisfactory results in productivity. The potential to reduce wellbore productivity while conducting drilling completion and workover procedures has The objective of this paper is to present a process designedto use the best available methodologies and been addressed extensively in petroleum related literature. laboratory techniques to assist in the design and selection of Productivity impairment was originally recognized in field fluids which will be most compatible with the reservoir. cases where development wens produced only small Ultimately the goal is to drill zero skin wells. The process volumes of fluid uponcompletion or where producing wells produced less after work-over procedures. In other addresses fluid design issues _from both a bridging or solid phase perspective and a liquid phase perspective instances, where drill stem tests taken while drilling deep wells indicated potentially goodproduction from shallow Optimization relative to design such as chemical selection zones, difficulty was experienced in attaining production and concentrations are an integral part of the process. from those zones which had remained in contact with Using this process will reduce uncertainty regarding fluid muds for anextended time.' Investigations of specific selection and the impact of the fluids on productivity. damage mechanisms is an ongoing pursuit. Bates et al Ultimately it is meant to assist in both increasing well discussed the influence of clay content on water conductivity productivity and reducing the requirement for expensive of oil sands in 1946.' Nowak et al studied the

THE PETROLEUM SOCIETY PAPER 97·114

Fluid Design to Meet Reservoir Issues­A Process

J. MasikewichQ'Max Solutions Inc.

B. BennionHycal Energy Research Laboratories Ltd.

This paper is to be presented at the 48th Annual Technical Meeting of The Petroleum Society in Calgary, Alberta, Canada, June 8 - 11,1997. Discussion of this paper is invited and may be presented at the meeting if filed in writing with the technical program chairman priorto the conclusion of the meeting. This paper and any discussion filed will be considered for publication in CIM journals. Publication rightsare reserved. This is a pre-print and is subject to correction.

'ABSTRACT

As open hole completion's, horizontal wells, multi-lateralsand underbalanced drilling become more common place,greater emphasis is being placed on the selection and designofdrilling and completion fluids. The problem ofassessingfluid compatibility with hydrocarbon reservoirs is ongoingand usually unique to each reservoir. This problem becomesmost visible after resources have been expended to drill, withunsatisfactory results in productivity.

The objective of this paper is to present a processdesigned to use the best available methodologies andlaboratory techniques to assist in the design and selection offlUids which will be most compatible with the reservoir.Ultimately the goal is to drill zero skin wells. The processaddresses fluid design issues from both a bridging or solidphase perspective and a liquid phase perspective.Optimization relative to design such as chemical selectionand concentrations are an integralpart ofthe process.

Using this process will reduce uncertainty regarding fluidselection and the impact of the fluids on productivity.Ultimately it is meant to assist in both increasing wellproductivity and reducing the requirement for expensive

stimulation. The process may lead to innovation - resultingin new systems or products. It may be applied whendesigning workover and completion fluids or for drill-influids including overbalanced or underbalancedapplications.

INTRODUCTION

The potential to reduce wellbore productivity whileconducting drilling completion and workover procedures hasbeen addressed extensively in petroleum related literature.Productivity impairment was originally recognized in fieldcases where development wells produced only smallvolumes of fluid upon completion or where producing wellsproduced less after work-over procedures. In otherinstances, where drill stem tests taken while drilling deepwells indicated potentially good production from shallowzones, difficulty was experienced in attaining productionfrom those zones which had remained in contact with drillingmuds for an extended time.1 Investigations of specificdamage mechanisms is an ongoing pursuit. Bates et aldiscussed the influence of clay content on water conductivityof oil sands in 1946.2 Nowak et al studied the

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effect of mud filtrates and mud particles on permeability in195e Various models which consider formation damagehave ~uantifiable outputs such as Skin Effect,4 ProductivityIndex and Formation Damage Index Number.6 Methods ofpreventing formation damage continue to be tested,developed and documented.

A greater percentage of wells are now designed as openhole completions, where perforating past the damaged zoneis impractical. Consequently sophistication in fluids testingprocedures has increased and frequently operators test wholefluids against their rock. Often fluid samples are obtainedfrom multiple sources. Return permeability tests7 areregularly used to select the "best" fluid. Unfortunately, if anadequate candidate isn't found, the data are usuallyinsufficient to redefine the direction testing should take. Theprocess described herein helps to categorize and quantifydiscrete damage mechanisms. Fluid design is systematicallyoptimized for all damage issues such that ultimately the fluidis compatible with the reservoir.

In actqal practice the first line of defense againstformation impairment is to keep foreign fluids and solids outof the rock. Thus, when drilling overbalanced, designing anefficient sealing cake or "bridging system"S becomesessential. However the very nature of bridging systemsdenotes spurt loss associated invasion. Further, since theefficiency of any bridging sy.stem diminishes due to bothmechanical degradation and through pore throatheterogeneity, only the effective design of the base fluid willprovide assurance that the best overall fluid was chosen todrill the reservoir.

ASSUMPTIONS

The focus when designing any fluid whether it is ROP,borehole stability or reservoir compatibility may besubordinated to other criteria such as cost, safety,environmental acceptability and operational feasibility. Theprocess described in this paper functions independently fromother design criteria - assuming they have been met and thenet result is a safe, acceptable fluid. Further, the efficientexecution of the process depends on the quality of the teamimplementing it. A cross functional team or asset teamshould be assigned to the project. Representation shouldinclude geology, reservoir, geophysics, production,completions and drilling as well as special core analysis anddrilling fluids expertise.

REVIEW OF FORMATION DAMAGE MECHANISMS

Common formation damage mechanisms have been

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categorized in different manners by various authors.9 Theyinclude:

Fluid - Fluid Interactions

Emulsion blocking - a viscous suspension of twoimmiscible fluids (usually oil and filtrate) which physicallyrestricts flow. Emulsions may be stabilized by drilling fluidcomponents, particularly oil-wet ultra rmes, or asphaltenes.

Precipitates and Scales - caused by incompatibilitiesbetween filtrates and connate fluids or bydissolution/precipitation of mineral grains. Someprecipitates which could cause physical plugging include:CaS04, CaC03, CaF:z, BaS04, srC03, SrS04'

Parrafms and Asphaltenes - especially associated withunderbalanced drilling where the reductions in temperatureand pressure associated with the production of crude oilresult in asphaltic or waxy sludges being deposited on or inthe near-wellbore pore throat system. Asphaltenes act ascationic particles with a potential to oil-wet rock. Mixing ofincompatible oil-based filtrates with in-situ liquidhydrocarbons may also result in de-asphalting of theproduced crude oil in some situations.

Fluid - Rock Incompatibilities

Migrating Clays - kaolinite has a tendency to shear awayfrom pore throat walls and migrate and plug if interstitialvelocities and electrolytic conditions are adverse (i.e., pHabove 8.5 or low salinity). Other loosely attached in-situclays or fines may also be susceptible to migration.

Swelling Clays - include smectites and mixed layer claywhich expand when contacted by fresh or low salinity water­based filtrates.

Phase Trapping/Blocking - refers to adverse relativepermeability effects associated with the retention of invadedaqueous or hydrocarbon fluids.

Chemical AdsorptionlWettability Alteration - somepolymers in water-based fluids and surfactants in oil-basedfluids are able to physically adsorb onto rock surfacesplugging pore throats (due to their large size) or alteringwettability, substantially reducing permeability.

Solids Invasion - when pulverized drilled solids orcommercial solids (clays, weighting or bridging solids)become rme enough to enter into the pore throat system,permanent plugging can result.

Other damage mechanisms - include grinding andmashing of solids by the drill string, spontaneous countercurrent imbibition effectslO and glazing and surface damageeffects caused by insufficient heat conductive capacity ofcirculating fluids.

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